The present invention relates to a method of joining steel pipes during the laying of coated large-diameter steel pipes underground.
Generally, the laying of coated large-diameter steel pipes in the ground is accomplished by digging the required excavation and setting steel pipes in the excavation, digging a cavity of a large section around the joining part of the pipes, aligning the pipes in the excavation, performing a tack welding, accomplishing a regular welding on both the inside and outside of the pipes, subjecting the joined part and the adjacent portions to cleaning and anticorrosion treatments and then backfilling the excavations. The problem with this method is that a considerable time is required before the completion of all of such operations, and that while it is possible to backfill a large part of the excavation during the relatively early period of the laying, the special excavation around the joining part of the pipes must be left without backfilling for a considerably long period of time. In the traffic laden areas such as city areas, however, efforts have been required to minimize the time required from the digging of excavations until the backfilling thereof.
It is known in the art to internally weld the pipes in order to ensure speedy joining of large-diameter steel pipes laid underground or ensure speedy laying of steel pipes underground. But even in this method, an anticorrosion treatment of the uncoated portion in the pipe ends must be accomplished externally, and therefore the digging of a special excavation of a considerable width for such anticorrosion treatment is still required.